1. Field of the Invention
The invention relates to corrosion-inhibited aqueous solutions and particularly relates to corrosion-inhibited antifreeze compositions containing dicarboxylic acids useful as coolants in a heat exchange system such as the cooling system of an internal combustion engine.
2. Other Inhibitors Known in the Art
It is well known to use dicarboxylic acids as corrosion inhibitors in aqueous systems. For example, Jones in U.S. Pat. No. 2,726,215 teaches that dicarboxylic acids; namely, sebacic acid and azelaic acid, and their alkali and alkali metal salts are useful corrosion inhibitors in aqueous solutions. The use of a mixture of sodium sebacate (sodium salt of sebacic acid) and benzotriazole was disclosed as a useful corrosion inhibitor in engine coolants by G. Butler, et al. in "Inhibitor Formulations for Engine Coolants," British Corrosion Journal, Vol. 12, No. 3, 1977, pp 171-174.
U.S. Pat. No. 3,931,029 to Dutton, et al. teaches the use of certain unsaturated cycloalkylene dicarboxylic acids as antifreeze additives to inhibit corrosion of contacted solder alloys. Corrosion inhibitors containing an imidazoline derivative, a carboxylic acid or its metal salt and/or a phosphate are used for steel in brackish or acidic water according to Chemical Abstracts, Vol. 99, paragraph 126713x, 1983, which describes Japanese Kokai No. 58-84, 981. U.S. Pat. No. 4,382,008 reveals a corrosion-inhibited antifreeze containing a triazole, an alkali metal borate, an alkali metal benzoate, an alkali metal silicate and an alkali metal salt of a C.sub.7 to C.sub.13 dibasic organic acid. The use of sodium sebacate as a corrosion inhibitor in phosphatebased antifreezes is further seen in the Derwent Abstract of Week E14 for French Certificate of Utility No. 2,489,355 to Perrot.
The Derwent Abstract of Week K18 for European Patent No. 77,767-B teaches the use of water-soluble salts of dicarboxylic acids having at least three carbon atoms as antifreeze corrosion inhibitors. These acids are malonic, succinic, glutaric and adipic acids along with smaller proportions of C.sub.8 and/or C.sub.10 dicarboxylic acids. A mixture of a siloxane-silicate copolymer with an azole was found effective in reducing the corrosion of high-lead solder and aluminum in aqueous liquids according to U.S. Pat. No. 4,402,847 to Wilson, et al. U.S. Pat. No. 4,414,126 also to Wilson involves the use of alkali metal mercaptobenzothiazoles as effective inhibitors for the corrosion of high lead solder in aqueous systems.
Molybdates are also known corrosion inhibitors; see, for example, U.S. Pat. No. 2,147,395 to Bayes and U.S. Pat. No. 2,147,409 to Lamprey. Sodium molybdate is even known to inhibit corrosion synergistically with other additives such as sodium nitrite, amine borate, carboxylate, ethanolamine borate esters, fatty acid alkanolamides, sarcosinates, phosphates and phosphate esters. For examples, see M. S. Vukasovich, "Sodium Molybdate Corrosion Inhibition of Synthetic Metalworking Fluids," Lubrication Engineering, Vol. 36, No. 12, Dec. 1980, pp. 708-712 and M. S. Vukasovich, Rust Protection of Synthethic Metalworking Fluids with Nitrite Alternatives," Lubrication Engineering, Vol. 40, No. 8, Aug. 1984, pp. 456-462. The carboxylic acid salts used in the studies described by these articles are believed to be derived from monocarboxylic acids due to the prices for the commercial materials quoted in the articles and because they are not specified as dicarboyxlic acid salts. In addition, aluminum corrosion is permitted by these materials which is characteristic of monobasic acids rather than dibasic acids. As will be demonstrated, the carboxylic acid used should be dibasic rather than monobasic since the combination of the monobasic acid with sodium molybdate allowed excessive corrosion of brass.
There remains a need for the discovery of highly effective corrosion inhibitors for aqueous solutions, particularly those which come into contact with high lead solder, particularly in phosphate-based solutions.